Running wire to detached garage


I'm wiring up my detached garage for 220v/50amps for a TIG Welder and air compressor. The plan is to change the breaker in the main panel for the 220v/30amp to a dryer outlet that is not being used to a 60amp breaker. I'm planning on running some new 6 AWG copper wire, 8 AWG neutral, about 75 feet to the garage into a subpanel with a 50amp breaker.
My problem is the routing of the wire. The wire will start out from the main breaker, go up to the attic, down another wall, to the outside via a 1" Schedule 80 PVC piping. Here it will go into the ground, minimum of 18" deep. This is where I get stuck, the outside wall of the garage is surrounded by a 3 foot section of concrete. Is it permissible to run the PVC on top of the concrete floor to enter the garage wall?
Or is the only way to somehow cut the concrete and lay the pipe?
Thanks in advance!
Darius
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There may be a few other things left out, such as ground conductor, ground rods, and expansion couplings. Can you not come out of the ground at the garage and use an LB condulet to go through the siding?

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Thanks for the reply, I will be running a seperate earth grounding rod for the garage. I could come out of the ground but I would have to go across 3 feet of concrete before I get to the garage wall. I've never seen PVC just laid out across the ground on concrete before.
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xgtfour wrote:

Buy yourself a copy of the NEC code book (assuming you're in the US), there are quite a few things you've mentioned that don't match code requirements.
First off for a sub panel you need to run four wires, the two hots, neutral and ground, you can not rely on a separate ground rod at the garage (though you can add an additional ground there if you want). The neutral should be the same size as the hots, the ground can be slightly smaller (see code tables). You should be using schedule 40 PVC conduit, schedule 80 is rarely ever needed.
If the issue is that the concrete foundation wall of the garage is 3' high before you reach the wood / siding area, then yes, you can run schedule 40 PVC conduit up along the cement before an LB into the sided area. If it's in an area with the likelihood of being physically damaged you need to provide some additional protection around it, or use rigid metal conduit for that section. In some areas expansion slip joints are required where you transition from underground to a structure for protection from frost heaves.
It's not clear from your post whether you are intending to direct bury the wire, or continue the conduit underground. I strongly recommend conduit the entire way so you can re-pull wire if needed in the future. I also recommend a larger than minimum conduit size to provide for easier pulling and future upgrades. As a last thought, consider spending the money up front to just run a full 125A sub panel (max allowed by code), the cost difference is small unless it's a really long run and you'll appreciate having the larger capacity panel in the garage.
Pete C.
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The current NEC allows you to do it with a separate driven ground rod and no continuous ground from the main panel, but only under certain conditions, which include that NO other metallic conductors of any type go between the two buildings, such as water lines, telephone line, CATV, etc. You'd be better off just running the appropriate ground conductor along with the feeders. You will have to drive a separate ground as well, for the garage panel. If you are going to have three feet of exposed PVC on top of the cement, I would use Sch 80 for the extra protection, if not galv

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Thanks again for the replies. I'm not sure what I mentioned that was not up to code, not running a ground wire is OK because I don't have any other metallic conductors between the garage and the house, like mentioned above. If there is something else, please let me know. There is not a 3 foot wall, just 3 feet of flat concrete to the garage. I would have no problem going to metal conduit out of the ground except for this part of the code:
DO NOT USE EMT {electrical metallic tubing} IN DIRECT CONTACT WITH EARTH. Article 331-4-A-5.
Does that mean I can't use galvanized or anything else that would provide more protection than a plastic pipe?
I'm really amped, no pun intended, to get this wiring going so I can work on my big block turbo project.
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xgtfour wrote:

go check out how deep the 3' concrete walk is. It's probably not too deep. Dig down next to it and take a solid steel rod (such as a post-hole digger) and drive it under the sidewalk to the edge of the wall. Then drive down throught the walk (using the post-hold digger) until you get to the same spot. Slide conduit under the walk and join with conduit from the top. Then deal with the cosmetics of the hole coming up (fill with silicone caulk?).
I don't know if it meets code, but it would be safe. I'll let other deal with the code issue.
good luck.
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Certainly, if you could go under the concrete, it would be neater, but threaded galv or even sch 80 should be fine. Don't transition back from rigid to plastic though, once you make the change, continue it into the new panel. Although it is currently still legal to do so, I would strongly recommend running the ground conductor to avoid future problems

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The concrete is 4" thick, I remeasured from the ground to the inside of the wall and it's only 2 feet. I think my best bet is to tunnel underneath the concrete and drill the floor in the garage. I hope I can rent some tools from the local Home Depot for the drilling. Then I'll just run the PVC underground, come up through the floor, cover the opening with some caulking. This sound up to code?
What's the best type of wire for using inside PVC and through my attic?
As far as not running a ground wire from the main panel, I thought running one was not up to code and that I had to leave it out.
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Drilling the floor sounds like a good idea. You want to use THWN rated conductors. They will probably have other ratings as well, but be sure one is "THWN". Pulling your ground with the conductors is definately code, and the better method of doing the job

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xgtfour wrote:

One warning on tunneling under the sidewalk and garage - the perimeter of the garage foundation is in all probability a lot thicker / deeper than the 4" sidewalk. Be sure to check this in some accessible location first or you may be surprised when you tunnel under the sidewalk and then thunk into the garage foundation footer. Coming up on the outside of the garage is perfectly acceptable and may be easier.
Pete C.
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xgtfour wrote:

Have you thought about running overhead triplex cable? You'll need to maintain a minimum distance above the ground; depending on the details it's probably 12 feet. If you can do that, and meet whatever other local codes might apply, overhead wiring will easier than tunneling under concrete. #6 aluminum "Periwinkle" cable would work perfectly between the buildings.
Best regards, Bob
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zxcvbob wrote:

The one time effort to run proper conduit underground to the garage is vastly easier than the continuing nuisance of overhead wires, particularly if you have trees to trim.
Pete C.
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Thanks so much for all the answers. I did consider going overhead but I have kids and I just picture them messing with it. Same with running the pipe on the 2 feet of concrete walkway surrounding the garage, that's why I want to hide the wiring. I'll definitely dig under the garage before I drill the concrete inside. I've never drilled concrete, so I'm sure it is going to be an experience.
I'm going to run THHN because of it's additional capacity. Is there a good place to buy this wire online along with the PVC?
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Go to an electrical supply or even HD, but THHN is for dry locations only and can't be used in an underground conduit

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If you plan to transition to cable for the above ground runs at each end, you might want to just use a suitable type UF cable for the entire run, encasing it in conduit for the underground part.
Don Young
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xgtfour wrote:

Most of the THHN wire you buy lately is also rated "THWN-2"
Call the local electrical suppliers and find one that sells to the general public as well as to contractors. (Most of them will do that.) Go to the "Will Call" or "City Sales" desk and know what you want -- or at least know almost what you want. They will be helpful as long as you don't waste their time with a *bunch* of questions.
Best regards, Bob
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